Forging process and apparatus



Nov. 20, 1962 STRUGALA ETAL 3,064,507

FORGING PROCESS AND APPARATUS Filed NOV. 2'7, 1959 Jrgvenfors:

ite rates atet filice 3,064,5W Patented Nov. 20, 1952 3,064,507 FGRGINGPR$CES AND APPARATUS Alfred trugala, Dortmund, Willi Sporenberg,Dortmund- Apierbeck, and Heinz Schmidt, Dortmund, Germany,

assignors to Wagner 8; Co., Dortmund, Germany Filed Nov. 27, 1959, Ser.No. 855,632 Claims priority, application Germany Nov. 27, 1958 13Claims. (Cl. 78-9) The present invention relates to a process andapparatus for forging articles.

In particular, the present invention relates to a process and apparatusfor forging an article which after it is treated according to theprocess and apparatus of the invention is further treated so as to beformed eventually into articles such as hearing races, spring rings, orthe like, which are not of relatively large diameter.

In the manufacture of articles of this latter type it is conventional toinitially forge a member which is formed with a bore extending partlytherethrough, and thereafter this member is acted on by a suitable punchso as to have the wall portion which closes the bore punched therefromand thus to form from the member a tubular piece which may thereafter befurther treated until it is finally formed into annular articles such asbearing races, spring rings, and the like.

The present invention deals with a process and apparatus for formingfrom a blank the initially forged workpiece which has the bore extendingonly partly therethrough, and it is this workpiece formed according tothe process and apparatus of the invention which is further treated withmachines and processes not formnig part of the present invention.

At the present time when workpieces of this type are forged they have aburr, and not only is there a considerable loss of time and increase oflabor costs involved in eliminating the burr, but also the temperatureof the workpiece drops undesirably during the time that the burr isbeing removed. It is desirable to maintain the workpiece at the elevatedtemperature it has at the end of the forging operation in order tofacilitate the further operations such as punching out the wall whichcloses the bore, etc.

It is accordingly one object of the present invention to provide aprocess and apparatus suitable of forging a workpiece of the typereferred to above without any burr thereon, so that not only is there asaving in time and a saving in labor costs, but also the temperature ofthe workpiece will not fall during the time required to remove a burr.

Another object of the present invention is to provide a process andapparatus according to which the workpiece will be forged with extremelyprecise dimensions enabling highly accurate workpieces to be producedafter the wall portion closing the bore thereof is punched out, eventhough the initial blanks introduced into the forge vary somewhat intheir dimensions.

It is still another object of the present invention to provide a forgingapparatus which is simple and rugged and at the same time operates veryefficiently requiring no outside source of power beyond that which isnormally available for reciprocating the forging rams.

It is furthermore an object of the present invention to provide aforging apparatus which will enable the workpieces to be removed withoutdifficulty from the forging apparatus as soon as the workpiece isforged.

It is yet another object of the present invention to provide a forgingapparatus which can work efficiently with hydraulic fluid even thoughsuch a fluid does not have the capability of returning parts to theirinitial positions when the pressure drops.

The object of the present invention also includes the provision of astructure capable of accomplishing all of the above objects and at thesame time composed of simple rugged elements which are very reliable inoperation and which will have a long life during which a minimum amountof maintenance is required.

With the above objects in view the present invention includes in aforging apparatus a primary cylinder means and a piston slidabletherein. The structure also includes a secondary cylinder means and adie means at least part of which is carried by the piston which isslidable in the primary cylinder means. This die means when it is in anoperating position defines a closed space in which a workpiece isshaped, and the secondary cylinder means serves to guide a piercingplunger which will extend into the space of the die means when thelatter is in its operating position so as to form a bore which extendspart way through the workpiece. At least part of the die means isfixedly carried by the piston which slides in the primary cylindermeans, and a conduit means is provided for placing the primary cylindermeans and a secondary cylinder means in communication with each other atleast during the time that the die means is in its operating position.Finally, a means is provided for reducing the volume of the primarycylinder means when the die means is in its operating position so as toincrease the pressure of a fluid in the primary and secondary cylindermeans so as to advance the plunger into the space defined by the diemeans when it is in its operating position.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a fragmentary sectional elevational view of one possibleforging apparatus constructed according to the present invention; and

FIG. 2 is a fragmentary sectional elevational view of another embodimentof a forging apparatus according to the present invention.

Referring to FIG. 1 there is illustrated therein a reciprocable forgingram 1 which in a Well-known manner moves up and down according to agiven cycle in response to the rotation of a crank shaft. A primarycylinder means 3 is fixed to the ram 1 for vertical reciprocationtherewith, this primary cylinder means 3 having a flange 2 which isfixed to the ram 1 through any suitable means such as screws, keys, orthe like. A primary piston means 4 is axially slidable within theprimary cylinder means 3, and the piston 4 has an extension 5 of adiameter smaller than the interior of the cylinder 3 extending outwardlybeyond the latter, the cylinder 3 terminating at its bottom end, asviewed in FIG. 1, in an in wardly directed annular flange 7 engaged bythe shoulder 6 of the piston 4 to limit the downward movement of thelatter with respect to the cylinder 3. In the schematic illustration ofFIG. 1 the shoulder 7 and the cylinder 3 are shown as being integral,although these parts can actually be made of separate members fixed toeach other. The cylinder 3 is formed with a bore 8 serving as theconnection for a hydraulic conduit 9.

A die means is formed in part by a die member 10 shown in FIG. 1 asforming the lower end portion of the part 5 of the piston 4. In theschematic illustration of and this surface 11 engages a surface 15 of acomplementary die member 13 which is fixed to the work table of theforging press. The die member has an interior hollow space 12 and a diemember 13 has an interior hollow space 14, and when the die means 10, 13is in operating position the surfaces '11 and 15 press against eachother so as to form an interior hollow closed space 12, 14 in which theworkpiece is shaped. It is not essential to provide a separate diemember 13. Instead, a simple flat plate will sufiice and in this eventthe surface 11 simply engages the top surface of such a flat plate.

The structure of the invention includes a secondary cylinder means whichin the embodiment of FIG. 1 is formed by a bore 16 of the piston 4. Thedie 10 and the portion 5 of the piston 4 serve to carry for a verticalreciprocating movement a piercing plunger 18 which is fixed with apiston portion 17 sliding in the secondary cylinder means 16. Thepiercing plunger means 18 carries next to its piston portion 17 a collarwhich at its upper surface engages a shoulder within the portion 5 ofpiston, 4 at the bottom end of the secondary cylinder means 16, and atits top surface the collar 19 is engaged by the upper annular spring ofa stack of dished annular springs cooperating together to form a springmeans 20 urging the piercing plunger means 18 upwardly to the positionillustrated in FIG. 1. In the schematic illustration of FIG. 1 the parts17-19 are indicated as being of onepiece althoughin the actualconstruction the piercing plunger portion 18 itself is removable fromelement 19 and can be exchanged for other plunger portions as, forexample, by being threadedly screwed onto the element 19 at a centralbore of the latter.

An ejector sleeve 21 surrounds the piercing plunger 1-8 which isslidable through this ejector sleeve 21. This sleeve 21 is movable inopposition to the spring means 20. For this purpose the sleeve 21 isprovided at its top end, as viewed in FIG. P1, with an annular outwardlydirected flange 22 engaged by the lower annular spring of the stack ofsprings which form the spring means 20, and the flange 22 engages thebottom end of the chamber 23 in which the collar 19 and the spring means20 as well as the plunger 18 are located, this chamber 23 being formedin the interior of the portion 5 of the piston 4. As is apparent fromFIG. 1, in the rest position of the parts where the spring means 20 isexpanded to its initial stress shown in FIG. 1 the sleeve 21 extendsinto the hollow inner space 12 of the die member 10.

A forged workpiece 24 is shown in dotted lines in FIG. 1, the workpiece24 of course having a configuration determined by the configuration ofthe hollow interior space 12, '14 defined by the die means 10, 13 whenthe latter is in its operating position. It will be noted that theworkpiece 24 is not provided with a bore which extends all the waythrough the workpiece 24. Instead the workpiece 24 has a bottom wallportion 25 which extends across and closes this bore. It is not at allessential that this wall 25 have .a precisely determined thickness. Aswas pointed out above, the forged workpiece 24 is treated immediatelyafter it is forged by having the trans verse wall portion 25 punchedout, and for this reason there is no purpose in providinga wall 25 of aprecisely determined thickness. The exterior surface of the workpiece 24is composed of a pair of oppositely inclined :Erustoconical portions 26and 27 whose contour corresponds to that of the dies. The junctionbetween these frustoconical surface portions 26 and 27 is absolutelyfree of any bur-r. The inclination of the frustoconical portions 26 and27 is shown to an exaggerated degree in FIG. 1. Actually the inclinationis extremely slight and the exterior surface of the workpiece issubstantially cylindrical.

The structure of FIG. 1 operates as follows:

A blank in the form of a cubic or cylindrical block is cut with a lengthas precise as possible from a billet and after this blank, made ofsteel, for example, is heated to the forging temperature, it is placedon the die 13. The reciprocating forging ram 1 reciprocates up and downaccording to a predetermined cycle determined by a rotary crankshaftconnected to the ram 1 for moving the latter up and down, and :as the 1moves down with a workpiece placed on the die 13, the die 10 coop crateswith the die 13- to shape the workpiece according to the configurationof the inner surface of the hollow space 12, 14. It should be noted thatthe engagement of the blank by the die 10 while the latter approachesthe die 13 does not result in a complete filling of the interior space12, 14 by the blank. This complete filling of the space 12, 14 isprevented by engagement of the end face ll of the die 10 with the endface 15 of the die 13. When the die 10, and of course the piston 4therewith, stop moving downwardly because of engagement of the surface11 with the surface 15, the ram 1 together with the cylinder 3 continuetheir downward movement and the cylinder 3 therefore now slidesdownwardly with respect to the piston 4 so as to decrease the volume inthe interior of the cylinder 3 and thus increase the pressure of thehydraulic fluid in the cylinder 3. When this pressure reaches a givenvalue it will overcome the force of the spring means 20 and will resultin the pressure of the fluid in the secondary cylinder means 16 becominggreat enough to produce downward movement of 'the piston portion 17 ofthe piercing plunger means 18 which now moves downwardly while thespring 29 becomes compressed. Thus the piercing plunger 18 advances intothe closed hollow space 12, 14 and extends into the body of theworkpiece to cause the latter to fill out all of the space 12, 14 whichis not occupied by the plunger 18. While the plunger 18 is advancinginto the work material the latter engages the sleeve 21 and moves thelatter upwardly in opposition to the spring 20 until the bottom face ofthe sleeve 21 is flush with the top end of the space 12 of the diemember 10. This limiting of the upward movement of the sleeve 21 can beprovided through a suitable size of the spring 20 or by provision of asuitable unillustrated stop member fixedly carried by the portion 5 ofthe piston 4 in the chamber 23 in a position to engage the flange 22when the latter moves upwardly beyond the position shown in FIG. 1through a distance suflicient to locate the bottom face of the sleeve 21precisely at the elevation of the top end of the inner space 12. i

There will remain a lower wall portion 25 on the workpiece since thepiercing ram 18 does not extend completely through the workpiece, andall of the excess material which would otherwise form a burr, forexample, accumulates in the wall portion 25 whose thickness need not beprecisely determined, as was pointed out above. Inasmuch as the volumeof the blanks cannot be maintained constant the wall portions 25 of aseries of workpieces 24 will have difierent thicknesses. Thus, With theprocess and apparatus of the invention this wall portion 25 will takeover the function formerly performed by the burr in that the excessmaterial of the blank will be accumulated in the wall 25 rather than ina burr. It should be noted that while when a burr is formed thethickness of the workpiece will vary depending upon the size of the burrso that it is not possible to precisely maintain the thickness of theforged piece, this disadvantage is avoided with the process andapparatus of the invention. Inasmuch as the surfaces 11 and 15 engageeach other over their entire areas at all times the length of theworkpiece will correspond exactly to the length of the space 12, 14along the axis of the piston 4. Any variations will appear only in thethickness of the wall portion 25. For the purposes of the subsequenttreatment step according to which the wall portion 25 is punched out,the thickness of the latter is immaterial and the wall portion 25 ispunched out without forming any burr. Thus, with the process andapparatus of the invention the final workpiece, after the wall portion25 is punched out in a manner not forming part of the present invention,will have very precise dimensions.

It is apparent that the thickness of the Wall portion 25 will determinethe extent to which the piercing plunger 18 is advanced, since it is thethickness of the wall portion 25 which will vary with differences in thesizes of the blanks. When the plunger 18 has advanced through a distancesuflicient to cause the work material to entirely till all of the space12, 14 except that occupied by the plunger 18 itself, then the plunger18 will no longer be able to advance into the space 12, 14 and thepressure of the fluid in the primary cylinder 3 and the secondarycylinder 16 will increase. The hydraulic conduit 9 carries a safetyvalve which can be adjusted so as to prevent the pressure from exceedinga certain predetermined maximum value, and this safety valve which isdescribed below in connection with FIG. 2, will, when the plunger 18 canadvance no further into the space 12, 14 act to prevent the pressure ofthe hydraulic fluid from becoming dangerously high, and thus as the ram1 together with the cylinder 3 move through their dead center positionan excessive stressing of the parts is avoided.

During the initial upward movement of the ram 1 and primary cylinder 3from their bottom dead center position, the spring 20 expands as thevolume of the interior of the cylinder 3 increases so that the surface11 remains in engagement with the surface 15 during this initial part ofthe upward movement of the ram 1 and the cylinder 3, while the spring 20expands, and of course this expansion of the spring 26 will result inupward movement of the piston 17, collar 19, and piercing plunger 18with respect to the die member 10 and the piston 4. Only when theplunger 18 has reached, with respect to the piston 4, the positionillustrated in FIG. 1 does the die member 19 move upwardly with the ram1 and the cylinder 3 so as to separate the surface 11 from the surface15. However, at this time the spring 20 can still expand further bymoving the flange 22 downwardly so that the ejector sleeve 21 now ejectsthe forged workpiece 24 from the die member 10. Inasmuch as the diemember 13 is relatively flat the workpiece will not be retained by thedie member 13. The workpiece is now completely free and can be treatedfurther.

Referring now to FIG. 2, those parts which are identical with theembodiment of FIG. 1 are indicated by the same reference characters. Itwill be noted that in the embodiment of FIG. 2 the piercing plungermeans 18 is not carried by the die member but is instead arranged withinthe die member 13. The die member 13 in the embodiment of FIG. 2 formspart of the work table of the forging press and a sleeve 29 of a slidevalve 28 is fixedly carried by this work table. The outer sleeve 29 ofthe slide valve communicates with a conduit 30 which leads to thesecondary cylinder means 31 of the embodiment of FIG. 2, and also theconduit 30 leads to an expansion tank 32 where a body of air 33 islocated over the hydraulic liquid so that the body of air can expand andcontract as is well known. The secondary cylinder 31 is shownschematically as being one-piece with the die 13 which forms the worktable, but actually the secondary cylinder 31 is threaded onto the worktable. The same applies to the expansion tank 32 whose size and locationare illustrated only schematically. A nonreturn valve 34 communicateswith the tank 32 and this non-return valve 34 opens when the pressure inthe conduit means 39 is smaller than the pressure in the tank 32. Asafety valve 35 already referred to above in connection with FIG. 1,this being the safety valve which is connected to conduit 9 of FIG. 1 soas to determine the maximum pressure of the hydraulic fluid in theprimary cylinder 3 and the secondary cylinder 16, is illustrated in FIG.2 connected to the conduit 30 as well as to the tank 32 so that theliquid which flows through the safety valve 35 will enter into the tank32, and thus the hydraulic systems of both embodiments of the inventionare closed systems. The tank 32 is also included in the embodiment ofFIG. 1 and also cooperates with the safety valve and the non-returnvalve in the manner illustrated in FIG. 2, the non-return valve 34communicating with the conduit 9 in the embodiment of FIG. 1. Thenon-return valve includes an adjusting screw 36 which is very carefullyset so as to regulate the maximum pressure of the fluid at which thesafety valve will open. 33 is a body of air in the tank 32.

The slide valve 28 is formed at an intermediate region with an annulargroove 37 into which a bore 38 formed in the slide valve 28 empties.This bore 38 extends through the bar 39 which is fixed to the slidevalve 28 at the upper end thereof, as viewed in FIG. 2, and the bore 38communicates at its top end with the conduit 9 which leads through thepassage 8 into the primary cylinder 3, as described above. A bracket 40which is fixed to the ram 1 carries the bar 39.

The structure of FIG. 2 operates in the manner corresponding to thestructure of FIG. 1. The workpiece is of course placed within the areasurrounded by the top annular surface 15 of the die member 13, and thisworkpiece will become located in the space 12, 14 when the die memberIii engages in its bottom end face 11 the annular surface 15. Of course,after the surface 11 engages the surface 15 the continued downwardmovement of the primary cylinder 3 will result in an increase in thepressure of the fluid, and of course the workpiece may be initiallydeformed before the die member 10 engages the die member 13 while thesurface 11 approaches the surface 15. Thus, the continued downward movement of the cylinder 3 after the die means 10, 13 has reached itsoperating position will cause the fluid whose pressure is increased inthis Way to act in the secondary cylinder 1 on the piston portion 17 ofthe piercing plunger means 18. Of course, when the surface 11 is closeto and in engagement with the surface 15 the annular groove 37communicates with the conduit 30 so that at this time the primarycylinder 3 and the secondary cylinder 31 are in communication with eachother. Thus, the piercing plunger 18 will advance into the space 12, 14and the workpiece 24 will be forged in the manner described above inconnection with FIG. 1, the only difference being that the transversewall portion 25 which closes the bore willbe located at the top end ofthe workpiece rather than at the bottom end thereof, as illustrated inFIG. 1. As soon as the advance of the piercing plunger into the space12, 14 has terminated the continued movement of the ram 1 and thecylinder 3 down to and through their bottom dead center position will ofcourse continue to increase the fluid pressure and at this time thesafety valve 35 will automatically open so that the fluid can now flowfrom the cylinder 3 through the conduit means into the tank 32. Duringthe upward return of the ram 1 and cylinder 3 toward their top deadcenter positions the spring 20 will expand, as described above inconnection with FIG. 1, so as to return the piercing plunger 18 to itsstarting position illustrated in FIG. 2 and then the valve 34 will openeither because of the pressure of the body of air 33 or as the result ofthe action of an unillustrated return spring which may be provided inthe cylinder 3 acting on the piston 4 of the embodiment of FIG. 2 tourge this piston to the position illustrated in FIG. 2.

It will be noted that with the structure of the invention there is noadditional drive beyond the already -avail able drive for reciprocatingthe ram 1. The force which acts on the piercing plunger is derived fromthe downward movement of the ram 1. If desired the structure may bepneumatic instead of hydraulic, although the hydraulic arrangement ispreferred, and with the structure of the invention the fact that thereare no particular return springs with the hydraulic structure is of nomoment.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types offorging apparatus and process differing from the types described above.

While the invention has been'illustrated and described as embodied inhydraulic forging apparatus and process, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any Way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can be applying current knowledgereadily adapt it for various applications without omiting features that,from the:

standpoint of prior art, fairly constitute essential characteristics ofthe generic or specific aspects of this invention and, therefore, suchadaptations should and are intendedtobe comprehended within the meaningand range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a forge, in combination, primary cylinder means; a piston slidablein said primary cylinder means, the latter being adapted to have a fluidunder pressure therein; secondary cylinder means; a piercing plungermeans having a portion which forms a piston in said secondary cylin dermeans; die means forming a hollow space, when said die means is in anoperative position, with which said plunger communicates, said die meansincluding at least one die fixed with said piston which is slidable insaid primary cylinder; means providing communication between saidprimary and secondary cylinders when said die means is in said operatingposition thereof; and means cooperating with said primary cylinder forreducing the volume thereof when said die means is in said operativeposition so as to increase the fluid pressure within said primarycylinder and thus increase the fluid pressure within said secondarycylinder so as to advance said plunger into the hollow space of said diemeans to operate a workpiece.

2. In a forge, in combination, primary cylinder means; a. pistonslidable in said primary cylinder means, the latter being adapted tohave a fluid under pressure therein; secondary cylinder means; apiercing plunger means having a portion which forms a piston in saidsecondary cylinder means; die means forming a hollow space, when saiddie means is in an operative position, with which said plungercommunicates, said die means including at least one die fixed with saidpiston which is slidable in said primary cylinder; means providingcommunication between said primary and secondary cylinders when said diemeans is in said operating position thereof; means cooperating with saidprimary cylinder for reducing the volume thereof when said die means isin said operative position so as to increase the fluid pressure withinsaid primary cylinder and thus increase the fluid pressure within saidsecondary cylinder so as to advance said plunger into the hollow spaceof said die means to operate a workpiece; and spring means cooperatingwith said plunger for retracting the latter out of said space and forurging said plunger to a predetermined rest position.

3. In a forge, in' combination, primary cylinder means; a pistonslidable in said primary cylinder means, the latter being adapted tohave a fluid under pressure therein; secondary cylinder means; apiercing plunger means having a portion which forms a piston in saidsecondary cylinder means; die means forming a hollow space, when saiddie means is in an operative position, with which said plungercommunicates, said die means including at least one die fixed with saidpiston which is slidable in said primary cylinder; means providingcommunication be- 'tween said primary and secondary cylinders when saiddie means is in said operating position thereof; and means cooperatingwith said primary cylinder for reducing the' volume thereof when saiddie means is in said operative position so as to increase the fluidpressure within said primary cylinder and thus increase the fluidpressure within said secondary cylinder so as to advance said plungerinto the hollow space of said die means to operate a workpiece, saidmeans for reducing the volume of said primary cylinder including areciprocable forging ram which fiXably carries said primary cylinder.

4. In a forge, in combination; primary cylinder means; a piston slidablein said primary cylinder means, the latter being adapted to have a fluidunder pressure therein; secondary cylinder means; a piercing plungermeans having a portion which forms a piston in said secondary cylindermeans; die means forming a hollow space, when said die means is in anoperative position, with which said plunger communicates, said die meansincluding at least one die fixed with said piston which is slidable insaid primary cylinder; means providing communication between saidprimary and secondary cylinders when said die means is in said operatingposition thereof; means cooperating with said primary cylinder forreducing the volume thereof when said die means is in said operativeposition so as to increase the fluid pressure within said primarycylinder and thus increase the fluid pressure within said secondarycylinder so as to advance said plunger into the hollow space of said diemeans to operate a workpiece; conduit means communicating at least withsaid primary cylinder for supplying hydraulic fluid thereto; and safetyvalve means carried by said conduit means for determining the maximumpressure within said primary cylinder means.

5. In a forge, in combination, primary cylinder means; a piston slidablein said primary cylinder means, the latter being adapted to have a fluidunder pressure therein; secondary cylinder means; a piercing plungermeans having a portion which forms a piston in said secondary cylindermeans; die means forming a hollow space, when said die means is in anoperative position, with which said plunger communicates, said die meansincluding at least one die fixed with said piston which is slidable insaid primary cylinder; means providing communication between saidprimary and secondary cylinders when said die means is in said operatingposition thereof; and meanscoopei'ating with said primary cylinder forreducing the volume thereof when said die means is in said operativeposition so as to increase the fluid pressure Within said primarycylinder and thus increase the fluid pressure within said secondarycylinder so as to advance said plunger into the hollow space of said diemeans to operate a workpiece, said secondary cylinder means being in theform of a bore of said piston in said primary cylinder means.

6. A forging apparatus comprising, in combination, primary cylindermeans adapted to contain a fluid under pressure; a piston slidable insaid primary cylinder means; a worktable; a secondary cylinder meanscarried by'said worktable; a piercing plunger slidable in said secondarycylinder means; a reciprocable forging ram carrying said primarycylinder means; die means carried at least in part by said piston andhaving a closed position defining a space communicating with saidpiercing plunger; and conduit means part of which moves with saidprimary cylinder means, said conduit means providing communicationbetween said primary and secondary cylinder means when said die means isin said closed position thereof.

7. A forging apparatus comprising, in combination, primary cylindermeans adapted to contain a fluid under pressure; a piston slidable insaid primary cylinder means; a worktable; a secondary cylinder meanscarried by said worktable; a piercing plunger slidable in said secondarycylinder means; a reciprocable forging ram carrying said primarycylinder means; die means carried at least in part by said piston andhaving a closed position defining a space communicating with saidpiercing plunger; and conduit means part of which moves with saidprimary cylinder means, said conduit means providing communicationbetween said primary and secondary cylinder means when said die means isin said closed position thereof, said conduit means including a slidevalve composed of a stationary outer member and a movable inner member,said movable inner member forming the part of said conduit means whichis connected with said primary cylinder means for movement therewith.

8. In a forging apparatus, in combination, a die having a hollow spacein which a workpiece is shaped; a piercing plunger slidably carried bysaid die; an ejector sleeve also slidably carried by said die, saidplunger extending slidably through said sleeve; and spring meanscooperating with said sleeve for urging the latter to a rest positionwhere part of said sleeve extends into said space.

9. In a forging apparatus, in combination, a die having a hollow spacein which a workpiece is shaped; a piercing plunger slidably carried bysaid die; an ejector sleeve also slidably carried by said die, saidplunger extending slidably through said sleeve; and spring meanscooperating with said sleeve for urging the latter to a rest positionwhere part of said sleeve extends into said space, said sleeve having aflange engaged by said spring means and engaging a shoulder of said die.

10. In a forging apparatus, in combination, a primary cylinder; areciprocable forging ram carrying said primary cylinder; a pistonslidable in said primary cylinder; die means part of which is fixed tosaid piston; and stop means located in the path of movement of said diemeans during downward movement of said forging ram to stop the movementof said die means while said forging ram continues to move downwardly sothat said primary cylinder means will move downwardly with respect tosaid piston to reduce the volume of said primary cylinder means and thusincrease the pressure of a fluid therein.

11. In a forging apparatus, in combination, a primary cylinder; areciprocable forging ram carrying said primary cylinder; a pistonslidable in said primary cylinder; die means part of which is fixed tosaid piston; stop means located in the path of movement of said diemeans during downward movement of said forging ram to stop' the movementof said die means while said forging ram continues to move downwardly sothat said primary cylinder means will move downwardly with respect tosaid piston to reduce the volume of said primary cylinder means and thusincrease the pressure of a fluid therein; secondary cylinder means; apiercing plunger slidably carried by said secondary cylinder means andcommunicating with the interior of the die means; and conduit meansproviding communication between said primary and secondary cylindermeans at least when said stop means has stopped the movement of said diemeans so that during the continued downward movement of said primarycylinder means with 1G respect to said piston the fluid under pressurewill act in said secondary cylinder means on said piercing plunger toactuate the latter.

12. In a forging apparatus, in combination, a pair of die memberscooperating with each other to define a hollow closed space when saiddie members are in an operative position, said die members respectivelyhaving surfaces engaging each other when said die members are in theiroperative position; piercing plunger means slidably carried by at leastone of said die members for movement into the space defined by said diemembers when the latter are in their operating position so as to form ina workpiece a bore which does not extend completely through theworkpiece; and means cooperating with said plunger means for moving thesame into said space until the workpiece fills that portion of the spacewhich is not occupied by said plunger means, said means for moving saidplunger means into said space stopping the advance of said plunger meansinto said space when the workpiece fills all of the space which is notoccupied by said plunger means, so that there will be no burr formed onthe workpiece at the place where said pair of die members engage eachother.

13. In a forging apparatus, in combination, a pair of die members havingan operating position pressing against each other to define a hollowspace in which a workpiece is shaped; piercing plunger means slidablycarried by at least one of said die members for movement in said space;hydraulic means cooperating with said plunger means to advance thelatter into said space until all of the space which is not occupied bysaid plunger means is occupied by the workpiece with said plunger meansextending only part way through the workpiece; and safety valve meanscooperating with said hydraulic means to limit the pressure of the fluidacting on said plunger means to a value which will stop the movement ofsaid plunger means irrespective of the distance the latter has advancedinto said space when said space is filled by the workpiece except forthe portion of said space occupied by said plunger means, whereby theworkpiece will not have a burr,

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